The project is focused on studies of gene expression during development in Drosophila melanogaster. Mutations of the white locus, which encodes a product that has strong sequence similarity with ATP-binding membrane transport proteins including the product of the cystic fibrosis gene of humans, show a wide range of changes in expression and regulation. We have concentrated on a group that originated by insertion of the transposon BEL into the 5' region of the gene. The original mutant strain and its derivatives show unusual regulatory changes in white expression; all have partial repression of gene expression when coupled with zeste mutations, a locus encoding a transcription factor. The zeste mutations also exhibit a trans effect on normal white locus function by repressing expression of paired wild-type alleles. We are attempting to understand the mechanisms of transcription regulation by studying the transvection effects and the mutants that show similar repressed phenotypes in cis-arrangements. A working hypothesis is that these mutations modify binding sites for the transcription factor in ways that change DNA configurations that are important in transcription initiation. Another developmentally regulated locus being studied is echinus, a locus that plays a role in development of facets in the adult eye. The gene is being cloned and molecularly and genetically characterized.